Aspects of the disclosure relate to processes for identifying APs which provide signaling that is reliable for use in calculating mobile device location based on RTT.
Determining precise locations of mobile devices has become a very important function in recent years. For mobile devices, there are countless applications that use information about device location. For example, a map application can select appropriate maps, direction, driving routes, etc., based on the current location of the mobile device. A social networking application can identify other users within the vicinity based on the location of the device. Many other examples exist.
Different techniques for obtaining a position fix for a mobile device may be appropriate under different conditions. In an outdoor environment, satellite-based approaches, e.g., Global Navigation Satellite System (GNSS) techniques may be suitable, because the mobile device may be able to receive satellite-based positioning signals with specific timing requirements. Based on reception of such satellites signals, a position fix for the mobile device may be calculated. However, satellite-based approaches may not be suitable in indoor environments, because satellite signals are sometimes not strong enough to be received indoors.
In indoor environments, such as a shopping mall, airport, sports arena, etc., access point (AP)-based approaches are generally more useful for obtaining a location fix for a mobile device. The mobile device derives information based on signals sent to and received from APs. Different types of information may be obtained such as Received Signal Strength Indication (RSSI) and RTT. Such observations allow the mobile device to estimate its distance to each AP. The mobile device can then triangulate and estimate its own location, based the distances to different APs.
With the proliferation of wireless local area networks, there are often many APs (e.g., 500 APs) operating at any given moment within particular indoor environments. However, in general, calculating location based on RTT and RSSI is computationally intensive. It is often impractical to perform such calculations for all APs within the range of a mobile device, because of limited processing capabilities, power consumption, and memory resources. Furthermore, as a result of multi-path effects, poor positioning, AP mobility, weak or inconsistent transmission power, or AP clock drift, some APs provide signaling which is not a reliable source of information for location calculations.